Transient non-Hermitian skin effect

TL;DR

This paper demonstrates that the non-Hermitian skin effect can be observed in passive systems using complex-frequency excitation, enabling the study of NHSE without gain media and revealing transient localization phenomena.

Contribution

It introduces a passive approach to observe the full evolution of NHSE using complex-frequency excitation, avoiding the need for gain media in non-Hermitian systems.

Findings

Exact NHSE persists in passive systems during a quasi-stationary stage.

Transient NHSE can be observed despite overall energy decay.

Localization of skin modes can be clearly witnessed and exploited.

Abstract

The discovery of non-Hermitian skin effect (NHSE) has opened an exciting direction for unveiling unusual physics and phenomena in non-Hermitian system. Despite notable theoretical breakthroughs, actual observation of NHSE's whole evolvement, however, relies mainly on gain medium to provide amplified mode. It typically impedes the development of simple, robust system. Here, we show that a passive system is fully capable of supporting the observation of the complete evolution picture of NHSE, without the need of any gain medium. With a simple lattice model and acoustic ring resonators, we use complex-frequency excitation to create virtual gain effect, and experimentally demonstrate that exact NHSE can persist in a totally passive system during a quasi-stationary stage. This results in the transient NHSE: passive construction of NHSE in a short time window. Despite the general energy decay, the localization character of skin modes can still be clearly witnessed and successfully exploited. Our findings unveil the importance of excitation in realizing NHSE and paves the way towards studying the peculiar features of non-Hermitian physics with diverse passive platforms.